Electric machines are utilized in a wide variety of applications. For example, hybrid/electric vehicles (HEVs) typically include an electric traction drive system that includes an alternating current (AC) electric machine that is driven by a power converter with a direct current (DC) power source, such as a storage battery. Machine windings of the AC electric machine can be coupled to inverter sub-modules of a power inverter module (PIM). Each inverter sub-module includes a pair of switches that switch in a complementary manner to perform a rapid switching function to convert the DC power to AC power. This AC power drives the AC electric machine, which in turn drives a shaft of the HEV's drivetrain.
As used herein, the term “multi-phase” refers to two or more phases, and can be used to refer to electric machines that have two or more phases. A multi-phase electric machine typically includes a multi-phase pulse width modulated (PWM) inverter module that drives one or more multi-phase AC machine(s). One example of such a multi-phase electric machine is a three-phase permanent magnet AC machine. In a three-phase system, a three-phase PWM inverter module drives one or more three-phase permanent magnet AC machine(s). For example, some traditional HEVs implement two three-phase PWM inverter modules and two three-phase permanent magnet AC machines each being driven by a corresponding one of the three-phase PWM inverter modules that it is coupled to.
In many conventional motor drive systems, the inverter modules are driven by switching vector signals that are generated based on voltage command signals. For example, in a conventional motor drive system that relies on closed loop current control techniques, these voltage command signals can be generated based on feedback or measured stator currents and current commands that are processed by a current regulator. To explain further, stator currents (Ia-Ic) from a machine are sensed, sampled, and transformed into synchronous reference frame currents. In addition, a torque-to-current mapping module generates current commands. A conventional torque-to-current mapping module is implemented using a set of lookup tables (LUTs) that are stored in memory (e.g., ROM). In such systems, the torque-to-current mapping module receives a torque command signal (Te*), an angular rotation speed (ωr) of the machine, and a DC input voltage (VDC) as inputs, and maps these inputs to current commands that will ideally cause the machine to generate the commanded torque (Te*) at a given machine speed (ωr). The synchronous reference frame currents and current commands are then processed at a current regulator to generate synchronous reference frame voltage command signals, which can then be transformed again, into stationary reference frame voltage command signals.
As such, these closed loop current control techniques rely on feedback, sensed or measured stator currents to generate voltage command signals that are needed to control the torque produced by the machine. However, in many situations, these closed loop current control techniques are not adequate or have to be modified. This can happen, for example, when one or more of the current sensors used to measure/sense stator currents are unavailable (e.g., when they fail or are known to be unreliable). In such situations, the feedback stator currents that are utilized in closed loop current control are not available, and therefore closed loop current control cannot be utilized to control the system.
However, it may be desirable to allow the operator of the vehicle to continue to drive the vehicle. This is sometimes referred to as a “limp home operating mode.” The electric machine(s) used to drive the electric vehicle can be operated with limited speed and torque ranges (that are less than would otherwise be normally available) such that the maximum speed of the machine and the maximum torque that can be produced by the machine are limited within restricted ranges.
It would be desirable to provide improved methods, systems and apparatus for mapping torque commands to generate voltage commands used to control a multi-phase permanent magnet machine. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.